A method of detecting voice activity in a digitally coded speech signal propagating in uplink direction for a mobile communication system , said coded speech signal comprising a representation of a spectral information and received at a receiver (4, 6) belonging to a control part (1, 3) of said system, in which said detection is performed by operating directly on the received speech signal and a signal representative of the presence or absence of voice activity is generated by submitting the speech signal to an energetic analysis, characterised in that said detection also includes a spectral analysis performed directly on the received coded speech signal, by exploiting only the spectral information contained in the received signal itself; and spectrum and energy information resulting from said spectral analysis and said energetic analysis, respectively, are jointly processed for generating said signal representative of the presence or absence of voice.